1. Field of the Invention
The invention relates to a circuit arrangement for a picture display device for generating a sawtooth-shaped deflection current having a trace and a retrace through a line deflection coil which during the trace period is connected to a trace capacitor by means of at least two series-arranged controllable deflection switches switched at the line frequency, said switches being non-conducting substantially simultaneously during the retrace period, the deflection coil, the trace capacitor and circuit elements which together form a retrace capacitance being part in said retrace period of a resonant network the elements of which determine the duration of the retrace period, the circuit arrangement also comprising a supply winding coupled to a supply voltage source for supplying supply energy to the resonant network during the retrace period.
2. Description of the Prior Art
Such a circuit is disclosed in U.S. Pat. No. 3,030,444. This prior art circuit has the advantage that the high voltage present across the deflection coil during the retrace period is distributed over two switches. In television receivers for which the known circuit is intended the line frequency has the value prescribed by the television standard, for example 15.75 kHz for the U.S. standard. For picture display devices for which a higher quality than for the now customary television receivers is desired a higher value may be opted for. This is particularly the case for picture display tubes having a high resolution which are used, for example, to display digitally generated pictures and wherein the line frequency has a value which may be located between 15 and 64 kHz.
The known circuit is also suitable for a line frequency other than 15.75 kHz, however on the condition that the supply voltage is given a different value so that also the trace voltage, i.e. the voltage across the trace capacitor and thereto gets a different value. Otherwise the amplitude of the line deflection current and consequently the width of the displayed picture would not be correct. If the line deflection circuit must be suitable for different values of the line frequency then the value of the supply voltage must be controllable, at least adjustable. Such an adjustment usually results in considerable losses. As, in addition, the supply voltage circuit which provides supply energy to the line deflection circuit usually has further loads which must not be affected by this adjustment, an adjustable, non-dissipative supply voltage circuit is difficult to realize.
The invention has as an object to provide a circuit of the above-mentioned type in which the amplitude of the generated line deflection current is substantially independent of the value of the line frequency and can be adjusted with simple, low-dissipation means to the desired value. According to the invention, the circuit is therefore characterized in that the supply winding is divided into at least two winding portions which are each connected by means of one end through a supply diode to the resonant network and by means of the other end to an associated deflection switch and are coupled to the supply voltage source via a controllable supply switch also switched at the line frequency, said supply switch being conducting during at least a portion of the trace period for storing supply energy in the supply winding when the supply diodes are non-conducting, and non-conducting during the remaining portion of the line period when the supply diodes are conducting, current flowing through the supply diodes during the retrace period replenishing losses.